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Abstract We demonstrate that 2‐alkenylarylaldimines and ketimines undergo thermal 6π‐azaelectrocyclization to generate a wide range of azabicyclico‐quinodimethanes (o‐QDMs). Theseo‐QDMs exist as a hybrid of a diene and a benzylic diradical. The diradical nature was confirmed by their ability to undergo dimerization and react with H‐atom donor, 2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) and O2. In addition, the interception of the diradicaloido‐QDMs by H‐atom transfer was used to synthesize five tetrahydroisoquinoline alkaloids and related bioactive molecules. The diene form can undergo [4+2] cycloaddition reactions with different dienophiles to generate bridged azabicycles in high endo:exo selectivity. The azabicyclico‐QDMs can be generated for [4+2] cycloaddition from a wide range of electronically and sterically varied 2‐alkenylarylimines, including mono, di, tri and tetrasubstituted alkenes, and imines derived from arylamine, alkylamine (1°, 2°, 3°), benzylamine, benzylsulfonamide andBoc‐amine.
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Intramolecular (4+3) Cycloadditions of Oxidopyridinium Ions: Towards Daphnicyclidin A
Abstract N‐alkylation of 5‐hydroxynicotinic acid esters with electrophiles containing diene functionality produces salts that undergo intramolecular (4+3) cycloaddition reactions upon heating in the presence of base. Initial studies used a three‐carbon tether to join the pyridinium ion and diene, revealing some aspects of the inherent selectivity of the reaction with such substrates. Much more challenging was the synthesis of related species possessing only a two‐carbon tether. Nevertheless, the cycloaddition of such compounds was successful, leading directly to the ABC ring system of the alkaloid daphnicyclidin A.
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- Award ID(s):
- 1764437
- PAR ID:
- 10446164
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- Volume:
- 28
- Issue:
- 41
- ISSN:
- 0947-6539
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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